1. Field of the Invention
The present invention relates to a method and apparatus for estimating the respective angular directions of one or more sound sources in relation to a specific position, and to a method and apparatus for using such estimated directions to detect when a moving sound source has moved through a specific angular direction and to monitor the sounds emitted from respective ones of a plurality of moving sound sources.
2. Description of the Prior Art
One method of estimating the angular direction of a sound source and of monitoring a sound source is described in Japanese patent HEI 5-114098. FIG. 22 shows the configuration of this prior art sound source direction estimation apparatus. In FIG. 22, first and second directional microphones 901 and 902 are set up spaced apart by a fixed distance L, along a line of flow of traffic. The sounds which are respectively gathered by these microphones, which can be referred to as traffic noise A and traffic noise B, are respectively amplified by amplifier circuits 903, 904, and the resultant signals are alternately selected by a changeover circuit 905, under the control of a timing control circuit 910, to be successively subjected to frequency analysis by a frequency analysis circuit 906. Frequency vector distributions SA and SB are thereby respectively obtained, corresponding to traffic noise A and traffic noise B. Next, the degree of similarity between the frequency vector distributions SA and SB is detected, and the time difference dt between the points at which the frequency vector distributions SA and SB become approximately identical is obtained, by a time difference detection circuit 908. A time difference/velocity converter circuit 909 then performs the calculation:V=L/dtto determine the velocity of the sound source, and displays this velocity value by a display circuit 911. In addition, the direction of the sound source can be calculated, based on the aforementioned time difference. In that way, with this prior art method, it is possible to estimate the angular direction of a sound source and to monitor the sound emitted from that sound source.
However with such a prior art type of sound source direction estimation method, when sounds from a plurality of sources are simultaneously reaching the microphones, or when there is a sound source other than the sound sources which it is desired to monitor, then the accuracy of estimating the direction of a sound source will become low.
In the following specification and appended claims, the term “direction” is to understood as signifying “angular direction with respect to a specific origin point”, unless used in referring to a direction of angular motion or direction of linear motion.